A power circuit used for an amplifier, which includes an amplifier provided with a linear amplifier serving as a voltage source, a DC/DC converter serving as a current source, a hysteresis comparator controlling the DC/DC converter, and a current detector detecting output current from the linear amplifier to output the detected output current to the hysteresis comparator; and a switching restricting device for restricting a switching interval in the DC/DC converter such that the switching interval is not equal to or less than a constant time or is not shorter than the constant time.